POWER FACTOR

WHAT IS POWER FACTOR

Power factor is a cosine angle between voltage & current.

Resistance is equal to Impedance   R=Z ie. True power = Apparent power

In AC ckt. V x I is apparent power & V x I x CosΦ is a true power

EFFECT OF LOW POWER FACTOR

Due to low power factor, current will increase and so copper loss will increase. If affects in decreasing the efficiency of the equipments.

Due to low power factor, voltage regulation of transformers, generators, switches and transmission line will increase but fault lever capacity will decrease. Due to this, loss of electricity will take place and for require load we have to increase the capacity of the equipments. To avoid this we have to provide capacitor bank in the line which will increase the power factor of the system.

EQUIPMENTS WHICH DECREASES POWER FACTOR:

Pumps, motors which are running on no load, Tube light, Fan i.e any inductive equipment. 

In AC circuit Power factor is important because power of circuit is equal to a multiple of voltage, current & power factor. And if PF of circuit is lowered, current increases for the same load. Due to which it affects consumer & Energy supplying centre.

Losses due to low PF:  Due to low PF, current increases for the same load. Equipments use for power wiring, will be of higher capacity and increases its size. In installation, resistive load like incandescent lamp, heaters, hot plates which works on unity PF, gives low output. Again if PF of load decreased, current will increase for the same power so energy meter will run fast and we have to pay more bill even though we are using less power.

If PF of installation of more consumers is low, current of transmission line increases, voltage drops  & terminal voltage decreases. Due to which voltage regulation of generator at generation station is to be maintained regularly.  Due to increase in line current, generator gets overloaded and heated. Due to increase in line current, size of line conductor is also to be increased, span of line pole to be decreased & so number of line pole to be increased. Due to increase in number of poles, there is increase in accessories. It results increase in distribution charges. In this,  supply company suffers.

Advantage of High PF:

1.      It helps for stable terminal voltage

2.      Better voltage regulation

3.      Power losses between transmission & distribution line decreases

4.      Efficiency of generating station increases and transmission gets cheaper.

5.      Conductors & accessories do not get heated.

6.      No need to use higher capacity accessories.

 VECTOR GROUP

By this we can know that how winding is arranged (Displacement angle 11 or 1)

Slip =     N_S – N_R    X 100

                 N_S

1.      DOL Starter gives 100% torque

2.      Auto transformer starter gives 60 to 85% torque

3.      STAR DELTA starter gives 1/√3 times i.e 50% torque

4.      SOFT starter : Frequency constant, voltage not less than 40%

5.      VFD: Frequency & voltage can be reduced at a time. Smoothly speed varied.

 CAPACITOR

Condenser: A condenser is a practical contrivance consisting of two conductors separated from each other by some suitable dielectric by which the capacitance of a conductor can be increased.

Common Dielectric materials used in condenser: Air, Paper, Mica, Ceramic, Oil etc

Dielectric strength: Dielectric strength is the maximum kilovolts per millimeter which an insulating medium can withstand without breakdown.

Effect of temperature to the dielectric strength: In reciprocal order the dielectric strength fails with the increase in temperature.

Dielectric strength = 1/Temperature

The increase of moisture causes lowering of the dielectric strength.

Storage of electricity by condenser: When a condenser is connected to a DC source an electric field is produced and the condenser gets charged. It retains the charge in electric field even when the charging voltage is removed and releases the charge when required. So it stores the electrical energy and releases when required.

 Capacitance: Capacitance is the property of a condenser by virtue of which it stores quantity of electricity in its dielectrics which is also defined as the ratio of the absolute magnitude of charge on either conductor to the potential difference between the two conductors. It unit is ‘F’.

Capacitance is depends on:

i)                    The common area of the conductor plates of the condenser,

ii)                  The distance between the conductor plates i.e. the thickness of the insulating medium an

iii)                The nature of the dielectric medium between the conductor plates.

Charging and discharging of condenser: When electrical energy is supplied to the condenser to store the electricity in the form of charge causing the increase of potential difference across condenser plates, then it is known as charging of condenser.

Time constant of a capacitor: Time constant of a capacitor circuit means the time during which capacitor voltage actually rises to 0.632 of its final steady value while charging the capacitor through a high resistance from a battery voltage. In other words it may be defined as the time during which the charging current falls to 0.37 of its initial maximum value.

Dielectric constant: The dielectric constant of a medium is the ratio of the capacitance of a condenser with the given dielectric medium between the plates to the capacitance of the same condenser with air (or more strictly vacuum) as dielectric medium between the plates.

Electrolytic condenser: It is a widely used condenser having large value of capacitance. It consists of two aluminum foils one with an oxide film and one without it, interleaved with a paper which is impregnated with a suitable electrolyte like ammonium borate.

Types: Wet type and Dry type.

Uses: These are used mainly for reducing the ripples in the rectified voltage waves. These are widely used in the power supply circuits of radio and TV circuits.

CAPACITOR CONNECTIONS ARE IN PARALLEL:

Our load is inductive & so PF decreases. To improve PF,  we have added capacitor bank on 3 ph. In Delta, per capacitor 440 volts are getting. In star 440 volts between two capacitors. Means in Delta I_L = I_ph √3 and in Star I_L = I_ph.  If capacitance is more (I_c), for same PF Delta connection is require.

PROTECTION RELAY (CAPACITOR PANEL):

1.      Under voltage relay

2.      Over voltage relay

3.      Auxiliary relay

4.      APFCR(Automatic Power failure control relay)

Advantages of Capacitors:

Ø  Switching surges are avoided thereby reducing maintenance requirement and wear-out of electrical switch gears.

Ø  Reactive power is compensated quickly; hence KVA demand can be reduced which results directly in reduced energy bills.

Ø  Protects sensitive electronic equipments, computers, PLC’s ets.

Ø  System P.F. can be maintained near unity to realize bonus from electric supply company.

Ø  It reduces losses and improves circuit load capacity.

Ø  Improves voltage regulation.

General Features:

Ø  High speed power factor correcting systems are designed to compensate the reactive power of any load requiring P.F. connection with minimum delay.

Ø  Renders distribution network is more stable since there is no contactor switching causing high voltage transients, harmonics and other disturbances.

Ø  Prevents voltage drop and flickering reduces failures in highly sophisticated electronic equipments like PLC’s computers and other control systems.

Ø  Helps in reducing maximum demand and KVARH consumption hence substantial reduction in electricity bills.

 How does capacitor behave if it is connected across (I) a DC supply, (II) an AC supply?

            (I) when connected across a DC supply capacitor will be charged to the applied voltage allowing no continuous flow of current during charging. It behaves like an insulator in DC circuit.

(ii)  When connected across an AC supply a current will flow continuously through the capacitor depending upon its capacitive reactance.

What do you mean by charging and discharging of a condenser: When electrical energy is supplied to the condenser to store the electricity in the form of charge causing the increase of potential difference across condenser plates, then it is known as charging of the condenser.

When a charged condenser delivers its stored electricity to a load resistance connected across the condenser causing the gradual cessation of potential difference across the condenser plates, then it is known as discharging of condenser.

Constant of a capacitor circuit: Time constant of a capacitor circuit means the time during which capacitor voltage actually rises to 0.632 of its final steady value while charging the capacitor through a high resistance from a battery voltage. In other words it may be defined as the time during which the charging current falls to 0.37 of its initial maximum value.

Coulomb: Coulomb is the derived S.I. unit of electric charge stored in condenser, defined as the quantity of electricity transferred by one ampere in one second which is proportional to the potential difference between the conductor plates.

Formula for energy stored in capacitor:  Energy stored in capacitor = ½ CV² jou8les, where C is the capacitance in farad and V is the applied voltage.

What types of condensers are used in single phase AC fan, motor, correction of motor power factor, radio, fluorescent tube light and ignition?

Fan motor	Paper type
Correction of motor power factor	Paper and electrolyte type
Radio	Air type
Fluorescent tube light	Ceramic or Mica type
Ignition	Mica type